The embodiments described herein relate generally to power augmentation of a gas turbine engine, and more specifically, to a method and system for augmenting the power of a gas turbine engine using steam injection.
A gas turbine is comprised of a compressor section that produces compressed air that is subsequently heated by burning fuel in a combustion section. The hot gas from the combustion section is directed to a turbine section where the hot gas is used to drive a rotor shaft, thereby producing shaft power. The shaft power is used to drive the compressor. Excess power not consumed by the compressor drives a generator that produces electrical power. The amount of power imparted to the shaft is a function of the mass flow and temperature of the hot gas flowing through the turbine, specifically the temperature at the inlet of the turbine.
When operating at base load, the firing temperature of the combustion gases at the inlet of the turbine is limited to an operational maximum to prevent degradation of turbine components. Specifically, if additional fuel were introduced to the system to increase the mass flow and turbine inlet firing temperature, and therefore the power output, the resulting increase in the firing temperature at the turbine inlet would potentially damage the engine. It is known that steam may be injected into a gas turbine engine to increase the mass flow through the turbine for power augmentation independent of an increase in firing temperature.
Traditional control systems controlled the firing temperature of the turbine by scheduling the exhaust temperature of the turbine to be a function of the compressor pressure ratio such that when the compressor pressure ratio increased due to the introduction of steam, the exhaust temperature, and therefore the firing temperature, of the turbine decreased to prevent degradation of the turbine components. However, modern control systems include models that estimate the firing temperature of the engine directly and enable the control system to schedule the firing temperature independent of the compressor pressure ratio and/or steam injection. In these modern control systems, the natural suppression that took place when firing temperature was a function of the compressor pressure ratio no longer occurs.
Therefore, it is desirable to provide a gas turbine into which large amounts of steam can be safely introduced in order to augment the power output of the turbine, and in which the firing temperature at the turbine inlet is suppressed to prevent degradation of turbine components.